The present invention relates to a method for identification of paper rolls and similar objects on various roll handling lines.
Paper rolls produced for various deliveries in a paper mill have different mass, diameter, and weight almost for each roll depending on what kind of rolls were ordered. Depending on for which consignment paper is produced, unit weight and consistency of paper in rolls vary, and clients have also different requirements on packaging. Generally for longer transporting distances tougher package is used than e.g. for domestic shippings. Those properties of a roll will be saved with the data of the client in a data system of the factory and for each roll an identifier is produced that can be used to connect the roll with its identification dam all the way from the manufacturing to the delivery to the client. In new systems various kinds of bar codes that are attached on the end of the roll core are used almost exclusively as identifiers at the moment.
On a roll packing line before a wrapping station is an identification station where the diameter of the roll is measured and the identification code is read. The measured diameter is compared with corresponding data in the identification code to ascertain that the identifier is correctly read and the roll coming to the wrapping station is the right one. To read the identification code, its location must be known, and the sensor reading the code has to be directed to the corresponding location on the end of the roll. Alternatively the code can be read by a scanning detector, e.g. by a laser beam, that wipes across all the end of the roll. For safety reasons the beam can not wipe over the edges of the roll's end. The diameter of the roll must thus be known.
U.S. Pat. No. 4,463,251 describes a method where the code reader head is directed on the location of the identification code by the diameter of the roll. In this method the bar code used as an identifier is situated on the center of the roll. The reader head is positioned by lowering the arm of the diameter measuring device onto the roll and stopping it there. The motion of the reader head and the diameter measuring device is synchronized e.g. by cogged belt transmission so that the path of the arm is halved for the reader head, in doing which a movement of the arm in length of the diameter of the roll is divided to the reader head's movement in length of the roll's radius. The movement of the arm is stopped by a limit switch and after that the location of the arm is measured. To identify the roll the diameter is compared with the identification code, after doing which type and amount of the wrapper can be reported to the wrapping station. This device is usually equipped with an ink-jet printer that prints so-called inner markings, e.g. arrow showing the direction of opening the roll.
The method for measuring the diameter utilizing a firm measuring arm is the most reliable method at the moment. The diameter is measured also by other means: ultrasonically, using photodetectors or other equivalent detectors. Common for all of the measuring methods is that the sensor is moved in relation to the roll and the movement is interrupted when the surface of the roll is detected. The reader head of the identification marking is directed on the center of the roll either synchronously with the measuring movement or utilizing a special moving and positioning device. The non-contacting measuring method is not capable to detect reliably measurement errors caused by loose paper.
This method of measurement has many disadvantages; the most important of them is the slowness. When the measurement arm and sensor are approaching the estimated diameter, the movement must be slowed down to avoid collision. Because the diameter can not be accurately estimated beforehand, the slowed motion will be long. That of course slows down the functioning of the station unnecessarily. The slowness of the measurement station may thus act as a bottle-neck on the fastest packing lines. If increase in the speed of the station is desired, the transfer speed of the measurement arm must be increased, for what additional sensoring, more powerful transfer devices and a complicated control mechanism are needed. The increase in speed will thus raise the price of the equipment but the benefit gained will be limited, however. If the movement of the reader head is synchronized with the diameter measuring device, the movement of the reader head can not be used to move the ink-jet printer, but the printer must have a separate moving mechanism. This adds to the number of the parts needed and complicates uselessly the construction of the device.